Method and apparatus for making film



Feb. 16, 1965 s. w. CHENEY ETAL 3,170,011

METHOD AND APPARATUS FOR MAKING FILM 2 Sheets-Sheet 1 Filed Feb. 14, 1962 5 v A1 1 1 5 M /2 4 V n. IIIHHIIIIIIIIIUMH QM A 1 2 a w m Z. N v m/ a I w whw 0 0 6 k W 1 mm w 4 0 2 5 Z Z 2 m 1 7 M i 2 m m fi TM!" m a Mk m n .1 am A a;

Feb. 16, 1965 c. w. CHENEY ETAL 3,170,011

METHOD AND APPARATUS FOR MAKING FILM Filed Feb. 14; 1962 2 Sheets-Sheet 2 me W m h Maw m M w a an 4 $5 m United statfisPatent 3110011 1 METHGD AND APPAiKA'fUS FOR MAKING FHQM Grant W. Cheney, Midland, Mich, and Frank '1. Hughes,

Rolling Hills, Califi, assignors to The Dow Chemical Company, Midland, Micln, a corporation of Delaware Filed Feb. 14, 1962,Ser. No. 173,270

, 31 Claims. (Cl. 264-95) 7 3,170,011 Patented Fears, 1965 It would be especially advantageous if a new and improved of film from polymers of non-aromatic or aliphatic 'hy-" drocarbon olefins, such as polyethylene, polypropylene and thelike.

It is advantageous to manufacture film of many thermoplastic resinous materials in tubular form. 'In such practice, it is oftentimes desirable (and may even be necessary) to orient the"'freshly extruded film simultaneous' with its Y extrusion by stretching it uniformly throughout th'e directions of its major dimensions. l

An efficacious technique for accomplishing such orientation utilizes the distending'elfectiof a trapped pocket or f 'bubble of gas which is enveloped .under pressure within the tubular film simultaneously with itsinitialformatiori. t

A tubulation process of this nature has been disclosedin' U.S. 2,461,975. US. 2,832,994 discloses another method of manufacturing film in this manner. Such aflproc ess has become known, andis frequently referred to, as the I ftrapped bubble process for the manufacture of tubular One of the paramount considerations involved in the manufacture of thermoplastic tubular film by the trapped,

bubble process is that of sizing and cooling the extruded tubing. Proper and efiicient coolingof the' freshly extruded tube simultaneouswith'or, actually, priortofits technique for the manufacture of film in tubular form in general accordance with the trapped bubble process could be provided to facilitate the preparation of film product, of an overall premium quality for'many of a varietyof thermoplastic film-formingmaterials. 1 It yvould be 'a pronounced advantage if tubular film could be produced, at significantly greately rates ,of production andwith. ma-

terially increased output from given apparatus installations without requiring changes in the die head and extrusion assembly of each particular tube manufacturing unit involved. I V

Therefore, the principal object of the present invention is to provide an improved method and apparatus for the preparation of tubular film from thermoplastic resinous materials.

A particular object ofv the invention to provide an improved method andappa'ratus for operation in general accordance with the trapped bubble process in which close and accurate temperature control and efficient and etficacious cooling of the freshly extruded film product prior to or simultaneous with stretching is readily achieved upon andin the tubular extrude. Y

- A further object of the invention is to facilitate the manufacture of. a uniform high quality and regularly constant guage (orthi ckness) film product. f

A still further object of the invention is to. facilitate the manufacture of thin walled tubular film having maximum strength and generally optimum physical properties andcharacteristicsa I A yet further objectof the invention is to manufacture a tubular film that is free from naturaland inherent "tendency, or at least has a minimum tendency, to block" I or cohere to itself when the tube is collapsed and/ or in subsequent processing or handling 'of the film.

An associated object of the invention is to provide a 1 method and apparatusfor the manufacture of tubular film in general accordance with the trapped bubble process wherein difliculties due to' inefficient and ineffective orientation is highly advantageous to secure optimum properties in the manufacturedfilrn product. It'has been proposed and it is known to employ air or other fgaseous fluid as a cooling medium for the freshly ex ruded film tube in the trapped bubble process using either external or internal, or both, circulation and c'ontactof the cooling fluid upon the tube during its orientation. US. 2,433,937;

2,668,323; 2,668,324; 2,697,852; and 2,844,846 are illustrative of various techniques and procedures that have been employed for cooling the freshly extruded film product during its orientation in the trapped bubble process.

It would be an advantageto provide a {new and'improved method and apparatus" for the manufacture of tubular film from "practically any desired. thermoplastic film-forming material capable of being utilized in the trapped bubble process wherein a'rnuch more precise and readily effective control of thetem'perature' and cooling of the freshly extruded fi lm could be achieved. It would V coolingprior to or simultaneous with orientation of the freshly extruded film tube might easily be avoided.

' Another object of'the invention is to provide afmethod I 1 and apparatus that are obviously well suited for the manu facture of continuous'filmtubes at high rates of production and with rnaximum'output from given apparatus installations. V I l 1 Still another object of the invention is to furnish a meth od and apparatusfor the production of film 'tube;wherein and whereby the prdduct maybe handled and collected after its manufacture with improved efficiency and enhanced results as regards appearance and unifo'rrnityff er the taken-up'rolls of film and disposition or lay of" thefilm product wrapped therein as well as to avoid variations ingage throughout the film.

A still; further object of the invention is to provideia new and improved method for the manufacture oftubu-f also be an advantage if filin' tubes could be manufactured i in such a Way that dimculty, or inferiority 'ofjproduct quality, orf'both, due toineificient and ineffective cooling L of the freshly extruded tube could be avoided. It would manufactured that are free from the tendency of the surfaces ofthe tube to block or adhere to eachother when the tubeiscollapsed'. It, would be of particular advantage if such a method arid means of'manufacturing filmtubes I be of further advantage and benefit if film tubes could be could beutilized for the production of tubular polyethylone and polypropylene film, aswell as in the'productigin'of manypot her; relativelythin gaugefilms comprised ofother desired; varieties of thermoplastic film-'forrningmaterials adaptableto'being utilized mine trapped bubble pieces lar film and apparatus means for its accomplishment capa:

ble, according to the trapped bubble projeess, of readily and'eas'ily providing excellentquality prodhct of optimum physical properties in a wide range of t'ub'e'diameters using -a given apparatus installation for the purpose. V Another significant object of the invention is to provide .an apparatus and method that wouldbe especially Well suited for the manufacture of various polyethylene, polypropylene and the likepolyolefin film in tubular form.

The foregoing and related objects are possibilitated by manufacturing a filmtubeof athermoplastic, resinous film-forming materialin a manner in general accordance with the trapped bubble process wherein a fused, thermoplastic film-forming, composition-is extruded intubular form. and distended b'y m eans of an internal gas bubble for iorientation of said freshly extruded film'tube prior to or the invention;

during the initial stages of its orienting distention and is cooled circumferentially on its internal and external surfaces by means of a radially and circumferentially impinging stream of air or other gaseous fluid at a temperature beneath the temperature of the freshly extruded thermoplastic material. p

The circumferentially impinging stream of air or other gaseous fluid within the extruded tube is directed radially outwardly from a centrally located distributor, with respect to the axis extrusion, somewhat in the manner of a pin wheel, so as to radially impinge on the inner cucumferential surface of the tube a radially directed stream that is constantly moving over the inner surface of the tube. a

The gaseous fluid, such as air, admitted in the radially directed stream for cooling the surface within the tube is under sufficient pressure to maintain distention of the hubble and accomplish the desired orientation of the freshly extruded film product.

While the air or other gasous cooling medium may be recirculated within the distended tube after it is radially impinged on the inner circumferential surface thereof and discharged directly to the atmosphere, it is generally advantageous for the cooling medium to be employed in a recirculated, closed, fixed volume system. Thus, the air or other gaseous cooling medium is cooled; radially di rected on the inner circumferential surface of the tube; withdrawn therefrom and recirculated after being warmed within the tube through an external gas-tight system which is physically located outside of the extruding area.

Further features and the'many cognate benefits and associated advantages of the invention are apparent and additionally emphasized in the ensuing description and specification, which, as it is described, is better understood with reference to the accompanying drawing, in which, insofar as is possible, like reference numerals are employed to indicate like parts, wherein: p

FIGURE 1 is a schematic representation, partially 1n cross-sectional elevation which, in part, is diagrammatically portrayed, showing the essential elements and combinations of one embodiment of the method and an apparatus for manufacturing tubular film in accordance with FIGURE 2, in fragmentary partially cross-sectional plan view, shows a similar extrusion in accordance with fl ring-like or annular orifice 14 of the tube die 10 to form the freshly extruded film tube 16 of the polymeric composition. Although in most cases it is satisfactory for the tube die .10 to have a circular or at least nearly circular orifice 14, it may also be suitably formed in oval, elliptical and other forms that are only generally circular in outline. The freshly extruded plastic film tube 16 is oriented simultaneous with extrusion by a distending gas bubble 79 which is trapped within the tube under sufficient pressure to cause stretching of the tube. The film tube 16 is advantageously (and usually) expressed along an extrusion center line that passes longitudinally through the center of the tube die 10. The film tube 16, after being oriented by the distending gas bubble '79, is withdrawn from the die 10 through a pair of pinch rolls 18. Advantageously, this is subsequent to passage through collapsing guides 80 (shown in FIGURE 7) which tend to flatten the tube film so that it may be more efliciently grasped and handled in the bight of the rolls 18. The nip or pinch rolls 18 (or their equivalent flattening means) may either be hydraulic stationary pressure rolls or driven rolls, dependingupon whether a mere collapsing or a forwarding and withdrawing action is dethe invention wherein the cooling gaseous fluid isrelayed v in a cooling system;

sired by such installation. The compressive effect of the nip roll pairs utilized for flattening the film tube should be light enough to avoid any undesired crushing or fusion reaction on the freshly extruded tube.

Although the film can be extruded in any direction, it 1s generally advantageous, as indicated in FIGURE 2, to have a vertically upward (or vertically downward) center line of extrusion.

The freshly extruded film tube 16 (upon its emergence from the die'and prior to or during its distention and stretching by the trapped bubble of gas 79)is cooled to a temperature beneath its' thermoplastic temperature or point of fusion by means of a radially directed inner circumferentially impinging stream of air or other gaseous coolant fluid, indicated generally by the reference numeral 20. The coolant stream 20 is directed against the inner surface of the film tube 16. The cooling air (or other fluid) is admitted through an inlet 26 under suitable pressure to maintain the distending gas bubble 79 as desired for the operation. After circulation and warming within the film'tube, the air or other fluid is withdrawn through an outlet 27.

Advantageously, as indicated, the outlet 27 is centrally and coaxially disposed within the fluid inlet 26. Like- FIGURE 3 illustrates, in cross-sectional plan, a typical diffuser for. effecting the cooling stream of gaseous fluid within the freshly extruded tube;

FIGURE 4 is a cross-sectional elevation of the difiuser as taken along the line 44 of FIGURE 3; Y

FIGURES 5 and 6, in elevation'and partially in section, illustrate varieties of driven-diffusers or self-impelled diffusers for directing the stream of gaseous coolant within the tube; and

FIGURE 7 schematically illustrates the practice of the present invention using an external cooling r1ng and an external contacting centering guide about the freshly extruded film tube. v With initial reference to FIGURE 1, there is schematically portrayed theessentials' of an operation according' as a fluid-forwarding and metering pump or its equivalent p It is generally advantageous, as specifically illustrated in FIGURE 2, to utilize cool air or other gaseous fluid .in a closed, substantially gas-tight system wherein the cool fluid is continuously introduced and withdrawn from the freshly extruded tube and recirculated through an external heat exchanging or the like system whereby the or an extruder screw or the like apparatus. The molten composition is extruded through the generally circular warm fluid withdrawn from the tubing is efliciently cooled -to a desired temperature by the'heat transfer medium pinch rolls 18 or by dilfusionthrough the thin wall 0f freshly extruded tube 16, it is generally advantageous to V the rotating motionsof the diffuser.

utilize a sensing device in the system which can accordingly detect anyv gas losses therein and, in turn, activate an increased supply of cooled fluid, such as air, to compensate for the loss. This maybe accomplished by use of. a width measuring device 33 cm the flattened sheet of tubing 19 as it iswithdrawn from the pinch rolls 18. This device is connected pneumatically,"by means of the tubes 35-36, to a pneumatically activated air (or other gaseous fluid) regulator 38 of any desired or suitable variety. 7

Thus, air regulator 38, in cooperation with'the width measuring device' 33, operates to control the flow ofcoolant fluid into the film tube through the inlet conduit 26 by means of the conduit 39 which communicates with the air regulator 38. Thus, in the event that any air (or' other gaseous fluid) is lostfrom the distending bubble 79, the diameter of the freshlyextruded tube 16 will lessen and cause the width of the flattened sheet 19 to diminish. This is sensed by the measuring] device 33.

which relates the information to theregulator 38 which, in turn, compensates for the; loss by allowing more air to be admitted to the interior of the tube through conduit 3% and the inlet conduit 26 to replenish the loss.

As indicated,a variable speedblower 42f in'the inlet conduit 26, is 'jutilized -to force the cooled gaseous fluid through the tube." Alternatively, if the pressure build-up in the distending bubble 79 is too great, the sensing device 33 (upon noticeableincrease in the width of the flattened tube 19)'relates' the information to the regulator 38' which 'fu'ser 221s positioned so as to be freely'rotatable about both air inlet 26 and air outlet 27. A packed hearing,

as discussed with reference to FIGURE 5, allows for low frictional rotation about air outlet 27. In like manner, diffuser 22 rests and rotates upon bearings 34 which are contained in bearing tray 37 attached to air inlet 26. The bearings may be of a packed variety thus preventing air leakage therethrough. Or, alternatively,'an independent packing or stuffing box arrangement may be employed for the purpose. Aligning ring 44, depending from the bottom of diffuserZZ, extends between bearings 34 to perform the two-fold purpose of keeping the diffuser in alignment and to assist in completing a seal against air leakage through the bearings. Although complete free dom from air leakage through the bearings is not essential, more etlicient operation is obtained if it is prevented or kept to a minimum. Rotation of the diffuser is provided from the moving air entering the diffuser from air inlet 26.

It is beneficial that deflectors of some sort be provided in the diffuser so that a tangential air motion creates the rotating thrust. For example, the arrangement of the curved vanes as illustratedin FIGURE 3 can-be used with advantage. I

In FIGURE 7 there areschematically shown several embodiments in accordance with the invention. Thus, an

external cooling ring is positioned around the outside of the freshly extruded film tube 16 to externally cool the "film tube 16 and thus provide an eflicient cooling of the in turn pneumatically relates the information through tube 43m (and to actuate) bleedoff valve 41. The resulting bleedoif of excess air from the system throughthe air restrictor- 4t and valve 41, as is apparent, automatically controlsand regulates the system.

In FIGURES 3 and 4 is illustrated aparticular diffuser i that is utilized in the practice of the invention. As indicated, diffuser 22 comprises a circularair-directing elea ment23. This element 23 contains aplurality of curved vanes 25 which extend radially from: the air inlet conduit 26 to the circumferential extremity of the air directing element. The'coolair stream 20 travels from the-air inlet 26 by way of inlet ports 28 to the passages between vanes 25 and exits from the element through apertures 24.' The warm air iswith'drawn-throughair outlet 27 as indicated by the directional arrowin FIGURE 4. "The diffuser may be made to rotate in the direction indicated by the'directional arrow in i-FIGURE 3 either by art-external power source or by the tangential movementof the air stream 2 9 If it is desired tof'utiliz'e a driven diffuser, FIGURES illustrates one embodiment convenient for the purpose.

In the device" illustrated, diffuser 22 is made'common with and aflixed' to air inlet 26 by wayofcollar21. ,This

is effected such' that 'no'leakage' offair isperrnitted between the diifuser and collar and that no slippage is-per 'mitted with respect of each other of th'eair inlet and collar. A -weld 'joint or a-bolted joint with suitable gasket i or packing" is beneficial. inlet 26 is connected 'to'a power drive mechanism (not showni generally external to the film tubeito provide rotation-of the air inlet and diffuser. I Conventional bushing or hearing, .stufling box or packing arrangements can be employed to allow rotation of the aii-{inl tze within thetubedie without leakage pf air from the filmftube. Packed bearings '32 are positioned '1 as indicated in order to allow'diffuser 22 torevolve about air outlet 27 with a minimum offriction. In this respect,

any adaptable roll or ball bearing maybe used.- The packing may be of any, suitable type that will preventor keep to a minimum air leakage through the bearing area.

Alternatively, an arrangement of a packing independent of the bearing can be used with advantage. Air stream 20 thus enters diffuser 22 from air inlet 26 and is centrifugally. accelerated outwardly through apertures 24 by With reference to FIGURE ,6, there embodiment of the invention; In this arrangeme'nt, difisa shownan illus-' tration of a self-impelled diffuser in accordancewith an tube in conjunction with diffuser 22. Cooling ring 12 is generally a ring having perforations through which air is directed at the film tube at a point not too distant from tube' die It) as indicated by the arrows in FIGURE 7.

Inthe preparation of the film tube in accordance with the invention, centering guides 15 maybe desirable and advantageous to keep the tube from becoming misaligned or wavering due to convection currents or such other disturbances. Any significant change in the alignment of the tube may cause material consequences infilmuniformitytdue to uneven cooling ofthe freshly extruded filnrtube. Collapsing guides initiate the collapsing of the film tube so that a rather gradual'depression iseifected- By the time the film tube enters the nip of rolls 18, it has approximately reached the maximum desired width of flattened'film tube 19.

It is generally advantageous for'the'radially impinging. stream of air (or other'gaseousfluid) 20, which is em ployed for internal cooling of the tube, to be. directed against the inner sidewalls of tube 16 at a radial distance as measured from the. peripheral "outlet apertures of the diffuser to the tube of between about A inch and 2 inches 7 and preferably between about andabout /2 inch and,

even more advantageously, not more than about inch.-

Beneficially, the cooling stream 20 is caused to impinge onl the'inner surface .of the tube at the point where disj' tention of .thefreshlyextruded tube is about commencing and at a point prior to, complete stretching and distention i of the tube, i.e., before, the tube has reached-its maximum g diameter. Generallygusing blow-up ratios between about 1 and 10 ,to 1, respectively. (more ordinarily, between about 2 and 5 to, 1, respectively), such a point occurs be.-

tween'about and 3orifice diameters along the center a line of extrusion frorn thefacerof tube ,die =10. Advantageously, the radiallyimpinging circumferentially con.-

tacting stream of cooling fluid 2i! is directed-on the inuertfi surface of the ."freshly extruded tubellfi at a distance (which, beneficially, is as small aspossible toobtain) whose length along'the center line of extrusion is also (consistent with the immediately foregoing discussion) not in excess of about 1 orifice diameter.

It is advantageous for thestream of cooling fluid 20 cooling stream and the relationship between the temperature of the cooling stream and the temperature of the extruded polymer. Ordinarily, between about 100 and 800, advantageously between 300 and 400 cubic feet of coolant (at standard conditions) per pound of polymer being extruded is employed with advantage. In this connection, particularly when polyethylene and polypropylene tubes are being manufactured, it is found to be generally advantageous for air to be utilized as the gaseous coolant and to employ it as a temperature not in excess of about 100 F. at a rate of about 400 cubic feet per pound of polymer being extruded into-films of thicknesses between about 0.1 and 25 mils. Alternatively for the sake of convenience, the rate of cooling stream directed to the internal surfaces of the film tube may be expressed in terms of the linealrate of extrusion of the polymer. Thus, advantageous, the gaseous coolant is introduced into the tube through the rotating diffuser at a rate that is in the neighborhood (giving or taking, say,about 20 or so percent) of about 1.67 cubic feet per lineal foot of film tubing having a circumference of about 7 feet (as is based on a film speed of about 60 feet per minute and a gaseous fluid rate of about 100 cubic feet per minute).

For the most part, the positioning of the external cool-' of the freshly extruded film that is achievedby the radially directed, internally circumferentially impinging rotating stream of temperature controlling gaseous coolant is especially instrumental in securing :such desirable film tubes. As is apparent, it readily permits extremely close and critical temperature regulation of the freshly extruded film tube leading to precise sizing and dimensional stabilityof the. film so prepared. 'Additionally," the accurate and uniform temperature control afforded by the invention significantly reduces the tendencyof the film to cohere to itself. This eliminates any great need to inject powder (or the like anti-blocking agent or dust) into the tube for such purpose. Furthermore, the desired effect (or effects) is (or are) efficaciously accomplished at a convenient point in the film manufacturing operation, even though thisiisone of the most crucial, criticahlsensitive and difiicult to control areas in the process.- In addition, as indicated,'the same sized extruder and die head assembly can be utilized in the practice of the invention to produce film tubes of excellent quality having an advantageously wide range of diameter. This obviously provides for a much greater flexibility in the manufacturing operation.

Therotating gaseous stream directed against the internal surface has a decided effect and beneficial influence on not only the efficiency of cooling, per se,.but also air-generally is directed on a limited area, or more air is delivered through one aperture than another for various reasons; with the' result being that portions of the tube become more rapidly cooled to lower temperatures than others. Streaks or varlationsin clarity and variations in film thickness and wrinkles or .puckers are created in the film product when such uneven cooling is prevalent V and obtained.

However, in the practice of the present invention, wherein a rotating cooling stream :is utilized, an even and equally distributed cooling of the film tube surface is alforded. This, at the least, achieves and accomplishes a complete randomization of any uneven cooling due to air (or other gaseous cooling fluid) being delivered through one or more apertures against the film tube at a greater voltune or velocity. Thus, any streaking or variations(s) in film gage or thickness or the like imperfections are randomly distributed throughout the film. -No malappearance of the film on the take-up polls is evidenced, Nor are there any formations of ridges, bulges and the like in the film from a build-up of layers of heavier gage in the same trans.- verse location along the length of the film.

Beneficially '(in this connection), in order to provide the uniform cooling and assure a thorough randomization effect, the rotating diffuser is made to rotate at a rate that is between about 10 and about 40 revolutions per minute per lineal foot of extruding polymer.

As indicated, practice of the present invention is particularly useful for manufacture of tubular film from polymers of nonaaromatic or aliphatic hydrocarbon olefins, such as polyethylene and polypropylene.

, carbon olefin polymers, for example, butylene polymers on the uniformity of the film. When n fixed or nonrotatable diffuser is employed, the impinging streatn of and copolymers of ethylene and propylene may be equally beneficially employed including both the conventional bnanch structured polythene type of polymer andlinear, high density (and so-called macromolecular) variety polymers, including those obtained in the Ziegler process.

Other of the normally solid film-forming thermoplastic resinous materials are also advantageously formedinto film tubes by practice of the invention. These, for instance, include: homopolymers of vinylidene chloride and copolymers of vinylidene chloride with vinyl chloride and/ or acrylonitrile. The invention is also Well adapted for practice when other haloethylene polymers such as polye vinylchloride, vinyl chloride/vinylacetate and other vinyl chloride copolymers, and so forth are extruded in tubular form in the indicated manner, as well as for such other halogen-containing polymer products as chlorinated polyethylene, chlorinated polypropylene,chlorinated rubber and the like. Still other of the film-forming resinous materials that may be conveniently utilized are styrene polymers, including polystyrene, film-forming copolymers of styrene with acrylonitrile, a-methyl-styrene, ethyl acrylate and the like mixtures-thereof as well as for various vinyl toluene polymers; acrylonitrile polymers, cellulose acetate,

cellulose acetate butyrate and other-thermoplastic, film.

forming derivatives of cellulose; polyarnides, including linear condensation products of adipic acid and hexamethylene diamine (nylon-66) and condensation products of epsilon caprolactani (nylon-6); film-forming polyesters including linear condensation products of terepht'halic acid andeth ylene glycol'and thelike polyesters; and other analogous thermoplastic resinous film-.forming-compositionsQ l The following examples further illustrate the-invention and are 'given for only such purpose without thought to thereby limit or otherwise define same Illustration A Other hydroegg, extruded into air at room temperature over a trapped air bubble which effected a blow-up ratio of about 1.8 to l of the film tube. On passing to the nip of a pair of collapsing rolls, the tube passed between collapsing. guides which tended to flatten the tube. The tube travelled about :feet from the die to the point of collapse. A 34 inch wide by 0. 0015 inch thick (double thickness) sheet of polyethylene was obtained. 7

In one instance (designated Run.-I), the tube was cooled by directing air against the external surfacelof the tube from a ring, circumscribing the tube, which was positioned about inch from the die. Air was supplied from the external ring to the tube at about 100 ohm. at a tem perature of about 70 3 In the second instance (designated Run II), a notating 11 inch diameter air diffuser of the, type represented .in FIGURE -3 of the drawing (power driven from a source external the tube) was positioned inside the'tube so that the diffuser rotated about an axis coincident with the axis of extrusion. This was employed in addition to (and conjunction with) the external cooling [ring used in Ron I. The diffuser was located about /2 inch from the die and its periphery was about /2 inch from the inner surface of the film tube about its circumference. The diffuser rotated about 140 rpm. and delivered to the internal tube surface about 50 c.f.n1.of air at about 40 LP. The air was delivered to'the ditfuserthroughthe annular space between coaxial conduits supportingthegdiffuser. The air 10 Illustration B In accordance utilizing the same polymer in preparing film in Run II of Illustration A, a film tubeewas prepared as follows:

The polyethylene was extruded at a temperature of about 400 F. through a tube-forming orifice having an outside diameter of about 4 inches'and an orifice'opening having a radial thickness of about 0.0020 inch. The blow-up ratio was about 1.9 to 1. A 12 inch wide by 0.0015 inch thick (double thickness) sheet of polyethylene was obtained'at about 18 1b./hour. A take-away rate of about 22.5 ft./min. was used. An external cooling ring was positioned around the tube-about /2 inch from the orifice and /2 inch firom the outside periphery of the film tube. Between and 75 c.f.m. of air at about 70 F. were delivered through the external ring to the external film surface.- As in Run II of Illustrationf A,

a rot'atableair diffuser was positioned within the film tube and rotated at about 120 r.-p.rn. from an external power source. FIGURE 3 of the drawing, which might be referred to as a squirrel cage type, having "a diameter of about 3 inches. It was positioned about /2- inch from the orifice inch from the internal film surface. Approxirntaielyi 35 c.f.m. of air at F. were deliveredthrough the dif fuser to theinternal film surface- "Thewarmed air was withdrawn, as in Run II of -Illustration A, through the axial conduit supporting the diffuserto an external heat exchanger' whe're it was cooled prior to being re-f I entered int'o the film tube.

trusion. In addition, immediately after passing through the collapsing rolls, the' flattened tube was-engaged by a Width sensing device operating-fin cooperation with the internal cooling air using a system like that described in the foregoing in connectionwith FIGURE 2 of theacl companying drawing.

' A' summary of the results of these two runs, 1 and lljis given in the followingtable: I l

it is thus quite apparent thatithe method of the'invention phoyides' for rnucli'higher'production ratesf' This in large measure, rn'ayj'be principally attributed to the significantly superior uniformity in gage throughout the filmf OfmRllIl Ilf -*'which allows 'forlfaster take-up speeds." Smooth, even rolls of film were obtained in. Run I1, whereas, in Run Ifuneven, rippled (and thusundesira ble) rolls of'filinwere obtainedtorcing'slower take-up speeds to be used in order to avoid splitting and tearing ofithe film. It was also observed that 'all of the inside surface of the" collapsed tube o'fRu n: I showed pronounced propensity-to. block :or cohere to itselfi In con trast, the collapsed tubeffofi Run II was essentiallycompletely free from any blocking'tehdency.

Furthermore, the overall width along the length. of the flattened tube of Run II was significantly more uni- The vflattened film tube had excellent clarity and was free of the tendency to block? It-also wasreadily subjected to further processing and handling treatments with out difficulty, it being of exceptionally uniform gage and texture.

In contrast, when tubular film sis prepared according to theimmediately foregoing procedure, excepting to utilize a simple conduit or pipe to deliver the cooling air into,

the film tube or to utilize a-stationa'ry diffuser or nozzle to deliver the cooling air into-the film tube, significantly inferior products result. These film tubes are charac- 1 terized in an undesirable tendencytoblock-and'in being of non-uniformity in appearance'and thickness, exhibiting streaks andthick-thin variations, which deter from the utility or" the filmand'interfere with subsequent processlng suchaas-roll take-up,.heat-sealing, laminating and such other operations to which the film,is;subjected.

of, other thermoplastic resins.

tered into in the practice of the present invention without substantially departing" from its'intendedspiritand scope." Therefore, his to be fully understood that the invention is not intended nor should it be considered to be'limited or in any manner restricted by or to. the delineated and preferred embodiments thereof which; are contained in the foregoing descriptionand specification. Rather, the

claims.

form than that of'Run I. This, superior width uniformity provides not only a more desirable and useful' product, but also eliminates waste when it'is desired to edge trim theflatten'ed tubeito obtain twoplanar sheets of the'filrn. 1

. 'What isiclaimd is:

1.-Method of" producing filin from jthermoplastic.

resinousfilm-fonningmaterial which comprisesz' (a) extruding a fused thermoplastic film-forming resin through a generallycircular extrusion orificejin a tube die inthe form "of a seamless. film tube; 1 (b) withdrawing said freshly extruded film tube away from saiddie fand radially expanding said tube overatrapped gaseous bubble'; 1 a flattening said expanded film tube with flattening means positioned at a distance from said die; (d) continuously applying to the exterior surface of with the same generaljprocedure and i The diffuser was of the type illustratedin The method and apparatus of the-invention'may also, 1 be utilized in the described manner-to prepare filmtubes @rttin changes andimodifications canfbefreadily en 11 I said tube, immediately after its extrusion and prior to its being expanded to its maximum diameter, a circumenveloping gaseous coolant stream at a temperature beneath the temperature of said freshly extruded film tube; and

(e) continuously applying to the interior surface of said tube, immediately after its extrusion and prior to its being expanded to its maximum diameter, a stream of gaseous coolant for the tube, which stream is at a temperature beneath the-temperature of said freshly extruded film tube and which is omniradially directed against the inner surface of the tube from a peripheral outlet within the tube while being'rotatingly swept thereon on a line about perpendicular to the axis of extrusion of said tube. v

2. The method of claim 1, wherein said thermoplastic film-forming resin is polyethylene.

3. The method of claim 1, wherein said thermoplastic film-forming resin is polypropylene.

4. The method of claim 1, wherein said thermoplastic film-forming resin is a copolymer of ethylene and propylene.

5. The method of claim 1, whereinthe radial distance of travel of said stream within said tube prior to initial cooling impingement against the inner surface of the tube is between about 'tinch and about 2 inches.

6. The method of claim 5, wherein said radial distanceof travel of the stream is between about V8 and /2 inch.

7. The method of claim 1, wherein said omniradially extending stream of gaseous coolant is applied to said interior surface of said tube at a distance from said extrusion orifice, as measured along theaxis of extrusion, that is between about /2 and 3 times the average diameter of the extrusion orifice employed.

8; The method of claim 7, wherein said distance from said extrusion orifice, as measured along the axis of extrusion, is about 1 orifice diameter and the blow-up ratio of said expanding tube in respect of said trapped gaseous bubble is between about 2 and to 1.

9. The method of claim 1, wherein said omniradially extending stream of gaseous coolant is applied to said interior surface at a temperature that is at least about 200 Fahrenheit degrees beneath the temperature of said freshly extrudedthermoplastic resin and ata rate of between about 100 and 800 cubic feet of gaseous coolant per pound of said extruded resin.

10. The method of claim 9, wherein the temperature of said gaseous coolant is between about 4 F. and about 40 F.

v11. The method of claim 1, and including the additional steps of: a Y

(f) withdrawing from the interior of said film tube said gaseous coolant after it hasibeen warmed;

(g) cooling said withdrawn gaseous coolant at a point external to-the extrusion area; and (it) subsequently recycling said cooled gaseous coolant into the interior of said tube in said rotating, omniradially extending stream of coolant fluid,

. said extrusion orifice, as measured along'the axis of ex-- said :withdrawing cooling and recycling of said gaseous coolant being accomplished in a'closed system. e

12. Methodof producing film from a thermoplastic perature beneath the temperature of said freshly extruded film tube;

(e) continuously applying to the interior surface of said tube, immediately after its extrusion and prior to its being expanded to its maximum diameter, an omniradially extending stream of gaseous coolant at a temperature beneath the temperature of said freshly extruded film tube from the periphery of a generally circular rotating diffuser, said diffuser rotating about an axis coincident with the axis of extrusion of said tube;

(f) continuously Wtihdrawing from the interior of said film tube said gaseous coolant after it has been warmed;

(g) cooling said withdrawn gaseous coolant at a point external to the extrusion area;

(It) recycling said gaseous coolant into the interior of said tube through the periphery of said rotating ditfuser,

said withdrawing, cooling and recycling of said gaseous coolant being accomplished in a closed system; and

(1') engaging said flattened film tube shortly after passing through said flattening means with width measuring means,

said width measuring means cooperating with said withdrawing, cooling andrecycling system in a manner whereby the size of said trapped gaseous bubble may be increased and decreased to a predetermined size by increasing and decreasing, respectively, the amount of gaseous coolant entered into said film tube.

13. The method of claim 12, wherein said thermoplastic film-forming resin is polyethylene.

14. The method of claim 12, wherein said thermoplastic film-forming resin is polypropylene.

15. The method of claim 12, wherein said thermoplastic film-forming resin is a copolymer. of ethylene and propylene.

16. The method of claim 12, wherein the radial distance from the periphery of said rotating diffuser to said interior surface of said tube is between about V inch and 2 inches.

17. The method of claim 16, wherein said radial-distance is betweenabout A; and /2 inch.

18. The method of claim 12, wherein said omniradially. extending stream of gaseous coolant is applied to said interior surface of said tube at a distance from said ex trusion orifice,.as measured along the axis of extrusion, that is'between about /2 to 3 times the diameter of said extrusion orifice.

19. The method of claim 18, wherein said distance from trusion is about 1 orificediameter.

20. The method of claim 12, wherein saidomniradially extending stream of gaseous coolant is applied to said.

interior surface of said tube ata temperature at least about 200 Fahrenheit degrees beneath the temperature of said freshly extruded thermoplastic resin and at a rate of between about 100 and 800 cubic .feet of gaseous coolant per pound of said extruded resin.

21. Apparatus for manufacturing film from thermo- J plastic resinous film-forming materials which comprises,

' 'in cooperating combination:

said tube, immediately after its extrusion and prior to 7 its being expanded to its maximum diameter, a circumenveloping gaseous coolant stream at a tem- '(a) a tube die adapted to extrude a seamless film tube;

(b) flattening means positioned a distance from said die for fiattening'saidfreshly extruded tube;

(0) an inlet and an outlet conduit passing through said die from without and into the space that is enveloped by said freshly extruded tube;

(d) a generally circular diffuser rotatably disposed on the extrusion side of said die so asto rotate about an axis coincident with the extrusion axis of said die,

said dilfuser beingfurther adapted to deliver from its peripheral edge a gaseous coolant to the in- 13 terior surface of a tube as it is freshly extruded from said die,

(e) a means of communicating gaseous fluid from the inlet conduit to said diffuser so as to permit delivery of a gaseous coolant to said diffuser; and

(7") means to withdraw warmed gaseous coolant from said film tube through said outlet conduit.

22. The apparatus of claim 21, including, in addition thereto and in combination therewith:

(g) means disposed without and circumferentially about a tube of film after it has been freshly extruded from said die that are adapted to deliver a gaseous coolant to the exterior surface of tube after it is freshly extruded from said die.

23. The apparatus of claim 21, including, in addition thereto and in combination therewith:

(h) gaseous fluid propelling means and means for cooling gaseous fluid at a point away from said die and interconnected with said inlet and outlet conduits so as to recycle used gaseous coolant from said outlet through said cooling means back to said inlet.

24. The apparatus of claim 21, wherein said inlet and outlet conduits are coaxially disposed relative to one another.

25. The apparatus of claim 24, wherein said conduits are coaxially disposed about on the center line of extrusion of said die and said diffuser is supported by and at the internal end of said inlet conduit. 7

26. The apparatus of claim 21, wherein said diffuser is so proportioned and disposed that the radial distance between its peripheral edge and the inner surface of a film tube after extrusion from said die is between about inch and about 2 inches.

27. The apparatus of claim 26, wherein said radial distance is between about A3 and about /2 inch.

28. The apparatus of claim 21, wherein the axial distance between said diffuser and said die is between about /2 and 3 times the diameter of said die orifice.

29. The apparatus of claim 21, wherein the axial distance between said diffuser and said die is about equal to the diameter of said die orifice.

30. The apparatus of claim 21, wherein said diffuser is adapted to handle between about 100' and about 800 cubic feet of gaseous coolant for each pound of resin that said die is adapted to extrude into film.

31. Apparatus for manufacturing film from thermoplastic, resinous, film-forming materials comprising, in cooperating combination:

(a) a tube die adapted to extrude a seamless film tube;

(b) means adapted to be disposed without and circumferentially about a tube of film freshly extruded from said tube die and further adapted to deliver a gaseous coolant to the exterior surface of said freshly extruded tube;

(0) flattening means positioned a distance from said die for flattening said freshly extruded tube;

(d) an inlet andan outlet conduit coaxially disposed relative to each other and passing about centrally through said die from without and into the space that is enveloped by a film tube when it is freshly extruded from said die;

(e) a generally circular diffuser supported by and rotatably disposed about said conduits so as to rotate about an axis coincident with the axis of revolution of said die,

said diffuser being further adapted to deliver from its peripheral edge a gaseous coolant to the interior surface of said freshly extruded tube, said inlet conduit terminating in cooperating relationship with said diffuser so as to deliver a gaseous coolant to the inside of said diffuser;

(f) recycle means comprising blower means and cooling means cooperatively interconnected to withdraw warmed gaseous coolant from said film tube through said outlet conduit, cool said warmed gaseous coolant and recycle it to said conduit; and

(g) width sensing means, located beyond said flattening means, adapted to engage said flattened tube and continuously measure its width,

said width sensing means cooperating with:

(h) a regulating means that is in working relationship with said recycle means and adapted to introduce to and bleed off from said recycle means saidigaseous coolant.

References Cited in the file of this patent UNITED STATES PATENTS 2,632,206 Pierce Mar. 24, 1953 2,641,022 Kress a June 9, 1953 2,668,323 Johnson Feb. 9, 1954 2,844,846 Kronholm July 29, 1958 I FOREIGN PATENTS 571,392 Canada Feb. 24, 1959 1,190,773 France Oct. 15, 1959 1,106,951 Germany May 18, 1961 

1. METHOD OF PRODUCING FILM FROM A THERMOPLASTIC RESINOUS FILM-FORMING MATERIAL WHICH COMPRISES: (A) EXTRUDING A FUSED THERMOPLASTIC FILM-FORMING RESIN THROUGH A GENERALLY CIRCULAR EXTRUSION ORIFICE IN A TUBE DIE IN THE FORM OF A SEAMLESS FILM TUBE; (B) WITHDRAWING SAID FRESHLY EXTRUDED FILM TUBE AWAY FROM SAID DIE AND RADIALLY EXPANDING SAID FILM TUBE OVER A TRAPPED GASEOUS BUBBLE; (C) FLATTENING SAID EXPANDED FILM TUBE WITH FLATTENING MEANS POSITIONED AT A DISTANCE FROM SAID DIE; (D) CONTINOUSLY APPLYING TO THE EXTERIOR SURFACE OF SAID TUBE, IMMEDIATELY AFTER ITS EXTRUSION AND PRIOR TO ITS BEING EXPANDED TO ITS MAXIMUM DIAMETER, A CIRCUMENVELOPING GASEOUS COOLANT STREAM AT A TEMPERATURE BENEATH THE TEMPERATURE OF SAID FRESHLY EXTRUDED FILM TUBE; AND (E) CONTINOUSLY APPLYING TO THE INTERIOR SURFACE OF SAID TUBE, IMMEDIATELY AFTER ITS EXTRUSION AND PRIOR TO ITS BEING EXPANDED TO ITS MAXIMUM DIAMETER, A STREAM OF GASEOUS COOLANT FOR THE TUBE, WHICH STREAM IS AT A TEMPERATURE BENEATH THE TEMPERATURE OF SAID FRESHLY EXTRUDED FILM TUBE AND WHICH IS OMNIRADIALLY DIRECTED AGAINST THE INNER SURFACE OF THE TUBE FROM A PERIPHERAL OUTLET WITHIN THE TUBE WHILE BEING ROTATINGLY SWEPT THEREONON A LINE ABOUT PERPENDICULAR TO THE AXIS OF EXTRUSION OF SAID TUBE. 